NEMA 14-50 amps question

[ldgrmnmc]

Very basic question for some, I'm sure, but I need help. I installed a NEMA 14-50 in my garage for my new model S. For the first month, I would charge it starting at midnight, and I would get 40 amp, resulting in about 30 miles of range per hour of charge.....in the last few days, without any other changes (that I know of), I'm only getting about 16 Amps, with a significant decrease, of course, in miles/hour charged....the setting on my big computer dashboard screen is still set at 40AMPs. Do I need to change something, or should I call my electrician? thanks, Lem

 

[Rocky_H]

The car's systems will back off the current for safety if it is sensing a resistive wiring problem. From 40, it will usually back it off to 30, to try it there. If there is still a problem, I think the 16A is the next step-down. You do very likely have a loose connection in your outlet install or at the breaker. You need to get that checked out.

 

[ldgrmnmc]

Thanks,,,,,since a week ago when I was having the desribed issue, my amps have jumped back up to 40.......electrician is checking it out today.

 

[mknox]

Or, it could be a utility supply issue. The way it works is the car sees a voltage drop and "assumes" it's a wiring problem or loose connection. If you are a considerable distance from the utility transformer supplying your house, the voltage drop may be occurring along the supply lines.

 

[scottm]

Take a peek when it's charging at night (from the app) and see what the volts are saying.

If the voltage drops, Tesla will kick down Amps until the voltage can come back up a bit.

If voltage drops too far... it gives up and stops charging.

On a 120VAC mobile charge, if voltage drops below 109 (I think), it gives up. I found this out at a hotel that had ancient wiring. Couldn't hold up to 110 for long. That sucked. I don't know what the give up point is for a NEMA 14-50 circuit that is supposed to be 240VAC.

Tesla may auto-re-raise the Amps if voltage comes back way up to what is normal and seems to be holding..

 

[ldgrmnmc]

The electrician didn't show up yesterday...ugh......scottm, I will check it out, and thank you!!

 

[SabrToothSqrl]

Mine drops all the damn time. It's PP&L. My wiring and outlet and UMC and all other crap are perfect. They've been over it 20x.

When my wife gets a 3, I'll make more of a stink w/PPL. They even put a monitor on my connection... down to the DAILY average volts. Because... that's frackin' useful...

With 2 cars pulling 40 amps each, heat pump, electric water heater, dryer, and whatever else I feel like turning on, I bet I can bend that 240v down... Maybe I'll put in a HPWC for fun. (I have dual chargers).

 

[grichard]

I've noticed that mine occasionally drops, but only in the summer. I suspect it's seeing a voltage drop associated with my house's AC compressor kicking on.

 

[brucet999]

I've noticed that mine occasionally drops, but only in the summer. I suspect it's seeing a voltage drop associated with my house's AC compressor kicking on.

…and those of all your neighbors, perhaps. The PoCo may be near capacity on hot days and reduce voltage to compensate.

 

[scottm]

Voltage dips are not doled out by the power company in response to heavy load, dialed down like a dimmer switch. Dips are a natural response (physics), quite an involuntary reaction to heavy draw... It's just what happens when the power feed is constrained in some way, and there's lots of reasons why that can happen.

The power company does have a say in power feed design and can engineer-in ways of having less drop under heavy loads at your house.

When I filed the permit to upgrade my house service from 100A to 200A, the power company upgraded the transformer at my pole and they pulled heavier wire (from 2/0 to 4/0 AWG) from the pole to my property line, and I continued that to my meter at the house. If all this didn't happen I would not likely be seeing 236VAC at 80A at my HPWC for the full 19kWh drink.

I didn't get a bill for the new transformer, pole work, or heavier gauge to the property line. That's on the utility, the power company does that for "free" (averaged over all their customers). They're happy to allow me to suck as much power as I can take and willingly bill me for doing so, all day long. Knock yourself out, they get you in the long run.

 

[brucet999]

Voltage dips are not doled out by the power company in response to heavy load, dialed down like a dimmer switch. Dips are a natural response (physics), quite an involuntary reaction to heavy draw... It's just what happens when the power feed is constrained in some way, and there's lots of reasons why that can happen.

Actually, voltage drops are sometimes done by the PoCo. They are called "brownouts".

Brownout (electricity) - Wikipedia, the free encyclopedia

 

[scottm]

..you are right about brownouts! Intentional voltage drops at the source.

I never consider those because we never have that occurring where I live.

I was talking about dips (sag) by over-demand on a fixed supply, which is what we'd see here.

And I see the words matter "drop" versus "dip". I should pay more attention to context. The PoCo can dole out a drop. Sorry bout that.

 

[SabrToothSqrl]

My guess guess is, being in a rural spot like I am, between my A/C, and everyone else's is when I have issues.. winter not as much.

 

[mikeash]

Are you pushing the plug into the car all the way? 16A is what it will do when you haven't pushed the plug in far enough to latch. It will show an orange ring rather than the friendly green ring when this happens, but if you insert it and walk away before it actually starts charging you could easily miss it.

 

[mknox]

I didn't get a bill for the new transformer, pole work, or heavier gauge to the property line. That's on the utility, the power company does that for "free" (averaged over all their customers).

That is not always the case, however. In my jurisdiction, the regulator will only allow utilities to "socialize" costs that benefit all customers. For things like this they perform an "economic evaluation" and charge the customer for the cost of improvements minus a factor reflecting the additional revenue they'll get from the larger service.